1. Field of the Invention
The present invention relates to ball catch couplings for rapid axial connection and release of two parts, such as two components of a dental handpiece, and which permits relative rotation of the parts with respect to each other in the connected condition. In particular the invention relates to a coupling having balls disposed at the circumference of one of the parts in a transverse plane contained in bores of a cylindrical section, the balls engaging an annular groove carried in the other part in the coupled condition.
2. Description of the Prior Art
A coupling device for dental tools is described in German patent No. 583,718 wherein the tool is driven by a flexible shaft and has a ball catch device having at least one catch ball which engages a catch groove in a separable part by means of a resilient open ring. The resilient ring has a plurality of catch bores at a circumference thereof which function to adjust the pressure acting on the ball. Automatic decoupling given overload of the two flexible shafts to be connected is achieved with this ball catch device. The catch device, therefore, does not function to permit fast axial coupling and decoupling of the parts, and further does not permit free rotation of the parts with respect to each other when connected.
Another ball catch device is described in U.S. Patent No. 4,431,412 wherein three spring-loaded balls are provided at the circumference of one portion of a handpiece, these balls engaging an annular groove at the circumference of the other handpiece part. The balls and the springs are held in place by a closed, non-resilient ring.
A disadvantage of such conventional ball catch devices is that the balls are pressed so tightly against the catch surfaces in which they are received during a catching operation as well as during an unlocking operation, such that the balls are no longer freely rotatable and are therefore drawn or scraped across the catch faces. Due to the lack of free rotation of the balls in this condition, the balls and the catch faces corresponding therewith are heavily worn given frequent coupling and decoupling.